Effect of metal pad instabilities on current efficiency in aluminium electrolysis

Uncompensated residual magnetic field in aluminium electrolysis cells leads to metal instability which is reflected as voltage instability referred to as voltage noise. The latter affects current efficiency and power consumption and has, therefore, a significant effect on the economy of the electrolysis operation. The characteristics of metal instability are studied in detail in this investigation by carrying out measurements related to voltage, magnetic flux, thermal energy loss and thickness of the frozen electrolyte (ledge). Current sinking method is employed to calculate counter electromotive force from which values for current efficiency are derived. These values are compared with those obtained from the copper dilution experiments. The studies indicate that unstable cell operation resulting from significant metal instability effect, due to unbalanced magnetic fields, leads to deterioration in ledge thickness, more heat loss and reduced current efficiency. © 2013 Indian Institute of Metals.